The present invention relates to an eye movement analysis system which measures the movement of eyes.
An eye movement analysis system (as disclosed in U.S. Pat. No. 5,196,873) which was devised by the inventor et al. of the present invention is already known. In this eye movement measuring system, a plurality of the light sources that emit infrared rays are arranged around the pupil of each eye, and these light sources are blinked. The pupil and iris striations are photographed. Horizontal, vertical, and torsional components of the eye movement are calculated from variations in the respective positions of the center of the pupil and the iris striations, whereby the eye movement is analyzed.
FIG. 6 is a block diagram of the aforementioned eye movement analysis system. The eye movement analysis system comprises a plurality of light sources 60 arranged around the pupil of each eye (E), a video camera 61 for photographing the eye E, and an image pickup means consisting of a video control section 62 for controlling the video camera 61 and a synchronous illuminating circuit 63 for synchronizing the blinking action of the light source 60 with a video signal. These elements are integrated into a pair of goggles. The image pickup means is further provided with polarizing filters F1 and F2 for eliminating irregularly reflected unnecessary light. The eye is exposed to infrared rays emitted as a result of blinking the light sources 60, and iris striations, the pupil and its surrounding are photographed.
The thus picked up image of the eye is recorded using a VTR (video tape recorder) 64 via the video control section 62. A time base collector 65 synchronizes an image signal with a synchronizing signal of an image signal processor, thereby resulting in a synchronous image.
An image signal processor 66 comprises a control circuit 66a for controlling the overall system, an analog-to-digital converter 66b for converting an analog image signal into a digital image signal, a frame buffer 66c which consists of a RAM for storing an image signal for one frame, a binary-coding section 66d which converts the image signal into binary digits, an image recognition section 66e which calculates the coordinates of the pupil and the iris striation, a computing section 66f which calculates the horizontal, vertical, and torsional components of the eye movement on the basis of the thus obtained coordinates of the pupil and the iris striation, and memory 66g for storing the result of the calculation. The image signal processor 66 is connected to a keyboard 67 for setting data having a required number of frames, a display 68 for displaying an image of the eye and the result of the calculation, and a printer 69 for recording the result of the calculation as required. The control circuit 66a has a built-in ROM (not shown), and a control program block of the control circuit is provided with a built-in program which displays a specification frame (a window) so as to surround the pupil and the iris striation displayed on the screen when the pupil and the iris striation are specified. As a result of specifying the displayed pupil and iris striation using the window, their coordinates on the screen are automatically calculated.
With the above mentioned configuration, processing is executed on the basis of a flowchart shown in FIGS. 7 and 8 when the eye movement is analyzed by photographing the iris striation and the pupil of the eye. Specifically, a subject wears a pair of goggles on his/her face, these goggles comprising the light sources 60, the video camera 61, and the video control section 62. A shutter speed of the video camera, the time period during which the light sources 60 are illuminated, and illumination timing for synchronizing the time period with the opening action of the shutter, are set with the keyboard 67 (step S1). Then, each eye is photographed (step S2), and the video control section 62 adds a time code to a resultant image signal (step S3). The image signal is then output and recorded in the VTR 64 (step S4).
The required number of frames, for example, 30 frames, is set by way of the keyboard 67 (step S5). The image of the eye reproduced by the VTR 64 is frozen at its first frame until the image processor receives a control signal from the control circuit 66a (step S6).
The image signal output from the VTR 64 is synchronized with a synchronizing signal of the image signal processor 66 by means of the time base collector 65, whereupon the thus synchronized image signal is output (step S7). This eye image signal is then converted into a digital signal by the analog-to-digital converter 66b of the image signal processor 66 (step S8), and the digital image signal is stored in the frame buffer 66c (step S9).
If the number of frames is n=1 (the first frame) (step S10), a window is displayed on the screen of the display 68 together with the image of the eye (step S11). The pupil of the eye and the iris striation to be measured are manually or automatically specified (step S12). In this case, the specifying action is only required for one frame. Further, it is possible to keep track of the pupil and iris striation with increased accuracy if a plurality of iris striations are specified.
If it has been judged in step S10 that the number of frames is not n=1, the processing proceeds to step S13 which will be described later. The data read from the frame buffer 66c are converted into image data (brightness data), corresponding to the brightness and darkness of the image, by the binary-coding section 66d.
While the respective positions of the center of the eye and the iris striation are specified, an image recognition processing section 66e track the center of the eye (that is, the center of the pupil) and the iris striation, by recognizing and processing one frame of processing data comprising bright and dark information, that is, one frame of binary-coded data, as binary-coded brightness data. The coordinates of the eye center and the iris striation are then calculated (step S13). The result of this calculation is stored in the memory 66g (step S14).
If the number of frames is different from the value (for example, n=30) set in step S5 (step S15), frames are automatically fed (step S16). An image signal for the second frame is reproduced by the VTR 64, and the processing returns to step S7. The image signal is then analyzed through the above mentioned procedures, and the processing is repeated up to the set n-th frame.
In this way, after the processing up to the set n-th frame has been completed, variations with time of the coordinates of the center of the eye in both horizontal and vertical directions, and variations with time of a torsional angle, are calculated from each of analyzed data items with regard to the eye and iris striation. As a result, the movement of each eye is analyzed (step S17), and the movement is displayed on the display 68 (step S18). The movement is then output to the printer 69 (step S20), as required (step S19). The analysis of the eye movement is now terminated.
However, the above described conventional eye movement analysis system automatically analyzes the position of the eye up to the preset number of frames, which makes it impossible for an operator to check whether or not a previously specified target iris striation has been actually specified in an analyzing step in which sequentially input iris striations are automatically recognized. For this reason, analyzed data may include data on the position of an erroneous iris striation, which leads to decreased reliability of the result of the analysis.